The virtual requirement that substance abuse programs use evidence-based treatments (EBT) has prompted the development of dissemination strategies to promote EBT technology transfer. Implementation research, clinical trial training methods, and clinician training studies suggest that clinical supervision that involves direct observation, fidelity rating-based feedback, and coaching of therapeutic skills is a promising dissemination approach. However, clinical supervision delivered within substance abuse programs by on-site supervisors has never been directly tested in a randomized controlled trial to determine the impact of supervision on both clinician EBT skills and client treatment outcomes. Recent results from two NIDA CTN protocols testing the effectiveness of Motivational Interviewing (MI) have shown that community program clinicians can learn to deliver MI with fidelity when receiving MI supervision from their program supervisors after workshop training and that their implementation of MI early in treatment improves client retention and primary substance use outcomes. A MI supervision manual called MIA: STEP (Motivational Interviewing Assessment: Supervisory Tools for Enhancing Proficiency) was developed from these protocols and has begun to be widely distributed by NIDA in partnership with SAMHSA for community program use. The effectiveness of the MIA: STEP supervision approach is unknown. This study will directly test the effectiveness of MIA: STEP supervision on clinician MI fidelity and on client outcomes by randomly assigning 60 clinicians and 420 substance-using outpatients from 12 community programs within Connecticut to one of two conditions in which clinicians in both conditions will deliver a 1- session MI intervention to clients as the enter treatment. The conditions are: 1) workshop training plus MIA: STEP supervision, and 2) workshop training alone with no supervision beyond standard supervisory practices used at each program. This project will be the first randomized trial to examine the impact of clinical supervision in an empirically based treatment on both clinician and client outcomes. Moreover, because it will provide workshop training and supervision completely within the context of community programs and utilize in- house program supervisors, it will provide a rigorous evaluation of a feasible model for disseminating EBTs such as MI. Public Health Relevance: This project will evaluate the effectiveness of clinical supervision in community substance abuse treatment programs. The project will determine if a newly released federally-supported supervision toolkit called Motivational Interviewing Assessment: Supervisory Tools for Enhancing Proficiency (MIA: STEP) results in 1) improved clinician skills in using an evidence-based treatment called motivational interviewing;and 2) increased client retention in substance abuse treatment and days of primary substance abstinence.